Ion mobility spectrometry or separation (“IMS”) represents a powerful method of separating and identifying ions, especially when coupled with liquid chromatography (“LC”) and mass spectrometry (“MS”) techniques. However, there are many instances where the IMS resolution is not sufficient to separate ions that have very similar Collision Cross Sections (“CCS”) or interaction cross sections.
The Collision Cross Section (“CCS”) or interaction cross section measured for a particular analyte depends on the nature of the ions produced from the analyte during or after the ionization process, and also on the conditions within the measurement device, such as the composition of the drift gas within an ion mobility spectrometry or separation device.
It is known to attempt to optimise the separation of ions in an ion mobility spectrometry or separation device for specific analytes. The optimal ion mobility conditions for a given analyte are determined by experimentally analysing the same analyte under each of several different conditions. However, this optimization is done empirically and involves a great deal of time consuming experimentation. Furthermore, this approach of non-directed experimentation may not ultimately lead to a satisfactory result.
Reference is made to Prabha Dwivedi, Brad Bendiak, Brian H. Glowers, Herbert H. Hill Jr. “Rapid Resolution of Carbohydrate Isomers by Electrospray Ionization Ambient Pressure Ion Mobility Spectrometry-Time-of-Flight Mass Spectrometry (ESI-APIMS-TOFMS)”. In this paper controlling the charge carrier during positive ion ionization of carbohydrates allows isomeric pairs to be resolved by ion mobility.
Reference is also made to: Rapid Commun. Mass Spectrom. 2009; 23: 3563-3569 “Use of ion mobility mass spectrometry and a collision cross-section algorithm to study an organometallic ruthenium anticancer complex and its adducts with a DNA oligonucleotide.” This paper illustrates an approach for calculation of theoretical cross section for known organometallic compounds.
It is desired to provide an improved method of mass spectrometry.